The present invention relates to molding compositions having improved properties. In a more specific aspect, this invention relates to molding compositions which, when molded, provide products with increased toughness. This invention also relates to a process for the manufacture of these molding compositions.
Molding compositions have been manufactured and used for many years in forming various articles. Examples of these compositions include sheet molding compositions (SMC) and bulk molding compositions (BMC).
However, the prior art molding compositions often experience problems with paint pops and edge pops on parts molded from sheet molding compositions. These problems can be attributed to the toughness of the resin contained in the SMC.
In further illustration of these problems, a molded part is commonly hot when removed from the press: After removal, the hot molded part is placed on a conveying device for movement to the next processing step (priming, painting, etc.) As the molded part is generally not handled gently during this process, there is an opportunity for microscopic cracks to form in the molded part. These micro-cracks are responsible for the paint pops and edge pops after the molded part is painted.
The toughness of the molding composition is generally achieved by careful selection of the building blocks of the molding composition. Currently, the toughness in molding compositions is imparted either by the addition of rubber particles or the use of vinyl esters in the molding compositions. Rubber particles are disadvantageous due to their need to be stabilized with emulsifiers to stay in homogeneous solution. Vinyl esters add cost to the molding compositions.
Examples of prior art efforts to improve the toughness of molding compositions include U.S. Pat. No. 5,116,917 (1992) which describes a thermosettable vinyl ester resinous composition and a low profile additive which is a non-gelling, saturated polyester.
U.S. Pat. No. 5,491,184 (1996) describes unsaturated polyester-modified flexible copolymers for use in sheet molding compositions.
U.S. Pat. No. 5,342,554 (1994) describes vinyl-terminated polyesters and vinyl-terminated polycarbonates which improve the flexibility and toughness of compositions made from unsaturated polyesters and fiber-reinforced plastics made from unsaturated polyesters.
Therefore, there is a need in the industry for molding compositions which will provide increased toughness to the molded products.
Briefly described, the present invention provides tough molding compositions for the manufacture of sheet molded products and bulk molded products. The present invention also provides a process for the manufacture of these tough molding compositions.
Accordingly, an object of this invention is to provide molding compositions.
Another object of this invention is to provide molding compositions for sheet molded products and bulk molded products.
Another object of this invention is to provide molding compositions which, when molded, provide products with increased toughness.
Still another object of this invention is to provide a process for the manufacture of molding compositions.
Still another object of this invention is to provide a process for the manufacture of molding compositions for sheet molded products and bulk molded products.
Still another object of this invention is to provide a process for the manufacture of molding compositions which, when molded, provide products with increased toughness.
These and other objects, features and advantages of this invention will become apparent from the following detailed description.